Reduced test case:

    struct Foo
    {
        Bar b;
        unittest
        {
            Foo f;
            f = Foo();
        }
    }

    struct Bar
    {
        ~this() @safe { }
        struct Inner { }
        Inner* i;
    }

As far as I can tell, the above is valid code, but when I run "dmd -c -unittest test.d", DMD spits out:

test.d(7): Error: function test.Foo.opAssign is not callable because it is annotated with @disable